As developments in electromobility have advanced, electrical safety considerations have also increasingly come to the fore. These relate on the one hand to the electrical risk potential emanating straight from the vehicle's own energy supply system. In electrical vehicles of the future, this on-board electrical system is usually designed as an insulated DC voltage system (high-voltage system) that supplies energy to the high-voltage consumers. Insulation faults can lead to system damage and cause high contact voltages that endanger individuals. On the other hand, since the electric vehicle's electrical energy stores are regularly charged, the risks occurring during the charging process of the electrical energy stores at a charging station must also be taken into account. In this case, a charging station may be located in the domestic environment or it may be a public charging station. Consequently, the network configurations of the power supply systems feeding the charging station and the resulting charging operating modes are also different. Hence, starting from earthed and unearthed power supply systems, different operating modes exist, such as single-phase and three-phase charging with AC or DC charging currents of different intensities. In addition, there are plans for charging stations that make it possible for energy to be recovered from the electric vehicle's mobile energy store into the stationary power supply network.
The combination of different power supply network configurations and the DC voltage network in the electric vehicle produce various requirements in relation to the electrical safety of the overall charging station/vehicle system. These safety challenges have hitherto been met by means of individual measures that are each separately implemented in the electric vehicle and in the charging station. Insulation monitoring and residual current devices are therefore adequately known and established for stationary power supply networks. Likewise, insulation monitoring instruments for hybrid vehicles have also be proposed that monitor the insulation level of their high-voltage systems.
Problems arise particularly when the electric vehicle is connected to the charging station for charging or recovery operation. As a result of the electrical connection between the electric vehicle and the charging point, a comprehensive earthed network with AC and DC voltage components results from the previously unearthed (IT) network of the electric vehicle in conjunction with a stationary, earthed (TN) current network. This shared network is usually monitored by a type A residual current device (RCD) fitted in the charging station that detects residual alternating currents and residual pulsating direct currents and is only allowed for pure residual direct currents up to maximum 6 mA, as higher residual direct currents can lead to functional impairment. When test currents are supplied by the vehicle's insulation monitoring instrument, (residual) direct currents may however occur that exceed the standard limit of 6 mA for a maximum permitted residual direct current and can therefore interfere with the function of the residual current device at the charging end. In the case of “unknown” electrical outlets, there is also uncertainty as to whether there is a residual current device in the electrical installation or whether the appropriate protection is guaranteed in the event of residual direct currents.
One disadvantage of the known protective measures that has therefore emerged is that they do not take full account of the special features of the respective network configurations and do not therefore exhaust the potential for comprehensive electrical protection against electric shock, particularly during the charging and recovery operation of the electric vehicle at a charging station.